Flexible circuits of various designs are known, in particular for low frequency or direct current applications. For example, commercially available flexible circuit strips such as used for computer printers are generally available in polyimide material film form such as KAPTON® material in thicknesses ranging from about 0.005 cm (0.002 in) to 0.013 cm (0.005 in). These flexible circuit strips are generally good for direct current applications where flex cracking of the metallized circuit lines can be accommodated without loss of signal capability. The material of these flexible circuits is more expensive in the thicker material form necessary for use when greater separation of metallization lines for alternating current or radio frequency or higher frequency signals are transferred. For example, the dielectric constant of KAPTON® material when metallization circuitry lines are closely laid for use in high frequency applications is particularly undesirable and produces higher signal loss.
In addition to the material considerations noted above, for applications in the X, Ku, K and Ka frequency bands, or when wireless communication signals generated for transmission or reception using phased array antennas are involved, it is often desirable to bond the flexible circuit(s) to a host device. Commercially available flexible circuits having an adhesive backing are generally unacceptable when formed and bonded to relatively small radii multi-conductor modules such as for phased array antenna applications. Commercially available multi-layer flexible circuits are also generally unacceptable for higher frequency use. When multi-layer flexible circuits are required, known systems suffer from cracking and signal crosstalk problems when used or bent to radii needed for the higher frequency small bend radii applications.